The invention relates to an antenna arrangement (flat antenna arrangement, plate antenna arrangement, patch antenna arrangement) with an earth plate and with a radiator which is arranged at a distance from and substantially in parallel to the earth plate and at one of its end zones is conductively connected to said earth plate, wherein at a first resonant frequency of the antenna arrangement a voltage minimum occurs at the connection point of the radiator to the earth plate and a first voltage maximum occurs in the region of the other end (free end) of the radiator.
Integrated antennae for mobile telephones based on the principle of the patch antenna are known. In existing applications the outer dimensions of such an antenna module are minimised for example by using a folded structure (e.g. C-patch). In addition to the single-resonance design (one single operating frequency band) other structures are known which facilitate operation in two defined frequency bands (such as for example in the two mobile radio communications bands of the GSM 900 and GSM 1800 standards). Here either two separate radiators are used or suitable measures are employed to provide that at the higher operating frequency only a specific part of the radiator is used. These procedures have the disadvantage that they do not utilize the whole of the available antenna volume, in particular at the higher frequency. As a result, the antenna has a small bandwidth.
The object of the invention is to develop an arrangement of the type referred to in the introduction such that it is suitable for two frequency ranges and permits a broadband construction.
This object is achieved, in accordance with the a flat antenna arrangement (plate antenna arrangement, patch antenna arrangement) with an earth plate and a radiator which is arranged at a distance from and substantially in parallel to the earth plate and at one of its end zones is conductively connected to said earth plate, wherein at a first (lower) resonant frequency of the antenna arrangement a voltage minimum occurs at the connection point of the radiator to the earth plate and a first voltage maximum occurs in the region of the other end (free end) of the radiator, in that at a further higher resonant frequency a voltage minimum and a second voltage maximum occur respectively at the foresaid ends of the radiator, and that the region of the free end of the radiator is capacitively coupled to another point of the radiator such that the further resonant frequency is reduced relative to three times the value of the first resonant frequency.
An advantage of the invention consists in that the entire radiator emits radiation in both frequency ranges. In this way a relatively large bandwidth is also possible at the higher frequency because a large radiator surface area is available. An advantage also exists at the lower frequency because here too the whole of the surface area available for the antenna can be used as radiator. One single point of the radiator can be used for the feeding.
In an embodiment of the invention, the capacitance value and connection point of the capacitive coupling are selected such that the second resonant frequency at least roughly approximates double the first resonant frequency. The suitability for operation in the 900/1800 MHz or 900/1900 MHz bands is advantageous.
In an embodiment of the invention the capacitance value and the other point are selected such that the first resonant frequency is reduced to a lesser extent than the second resonant frequency. It is advantageous that the dimensions of the antenna can be kept small.
In an embodiment of the invention the foresaid other point of the radiator, at which the capacitive coupling takes place, is situated in the vicinity of the first voltage maximum on the radiator at the second resonant frequency. A particularly large reduction in the second resonant frequency with a small reduction in the first resonant frequency is advantageous.
In an embodiment of the invention the foresaid other point is situated at approximately ⅓ of the unwound length of the radiator, measured from the connection to the earth plate. This dimensioning is favourable in many cases.
In an embodiment of the invention, the radiator at least partially has the approximate shape of a C, including an approximately C-shaped, non-circular, angular formation. This has proved favourable.
In an embodiment of the invention, the form of the radiator is selected such that the free end of the radiator is adjacent to a point of the radiator which corresponds to the desired other connection point of the capacitance. The short connection lines for the capacitor which are thereby facilitated are advantageous.
In an embodiment of the invention, the capacitive coupling is formed by a metal strip which, with an interposed layer of dielectric material, covers a part of the length of the free end zone and a part of the radiator at the other point provided for the capacitive coupling, such that the capacitive coupling is formed by a serial connection of two capacitors. The simple and space-saving construction is advantageous.
The invention also relates to a hand-held radiocommunications device, including transceivers, for at least one of the purposes: speech transmission, data transmission, video transmission, with an antenna, characterised by the fact that the antenna is formed by the antenna arrangement according to one of the claims substantially described above. It is advantageous that a simple transmitting/receiving circuit is possible. It is also possible for the device to possess a small structural form.
The invention also relates to a use of an antenna arrangement and a design of a hand-held radiocommunications device as referred to above. In accordance with the invention, only the second (higher) resonant frequency of the antenna arrangement is used in operation. This can lead to stockkeeping advantages if only the higher frequency band is required, but two-band antennas according to the invention are available.